From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Technical document detailing the Alumilite Process for anodizing and treating aluminium alloys.
| Identifier | ExFiles\Box 116\2\ scan0139 | |
| Date | 20th February 1940 guessed | |
| is maintained for 35 minutes, and is then raised during 5 minutes to 50 volts at which it is retained for the final 5 minutes. Direct current is used, the average consumption being about 2·8 to 3·5 amps. per sq. ft. of surface. THE ALUMILITE PROCESS is more flexible than the Bengough process, and may be used to produce films of varying hardness, thickness, etc., by varying the concentration of the sulphuric acid electrolyte between 7 and 35 per cent. according to the type of oxide film required. This treatment is carried out with the bath at 18±2° C. with a voltage of 10-20 volts D.C. and a current consumption of about 10-20 amps. per sq. ft. of treated surface. The time of treatment varies between 10 and 50 minutes. The oxide films thus produced have a cellular structure of a sub-microscopic nature, and to obtain maximum protection from corrosive agencies they should be sealed with an impregnating material. In the Bengough process the film is sealed by the application of lanoline or similar material as a solution in petrol; films produced by the Alumilite process are immersed in boiling water containing a suspended insoluble inorganic salt such as barium sulphate or in an aqueous solution of boric acid. In this connection it may be noted that by adjustment of solutions, temperatures, etc., in the Alumilite process, it is possible to give controlled conditions of the 25 per cent. sub-microscopic porosity which is claimed to afford complete protection against surface stress. Apart from their ability to provide a high degree of corrosion resistance, these anodically produced oxide films, which are normally colourless, by virtue of their high property of absorption may be immersed in water solutions containing suitable colouring compounds, to provide a wide variety of brilliant colours which are readily absorbed by the oxide films. The dye penetrates through the coating giving deep, rich hues, which have an underlying metallic sheen, making them unique and attractive for decorative purposes.† After this process of dyeing, the films may be given a sealing treatment as previously described. The oxide films possess several other important properties apart from those already mentioned, among them being high electrical resistance. The Bengough films will withstand 100 volts, while normal Alumilite films will withstand 500 volts and specially produced films have shown a resistance in excess of 3000 volts. The films are extremely hard and smooth, and are therefore used in some instances to increase the wear resistance of aluminium alloy parts such as pistons for internal combustion engines. Equally important in this connection is the porosity of the surface of these films, which aids materially the retention of the lubricant.‡ The porous unsealed films provide an excellent base for paints, the adhesion between paint and metal being remarkably strong. *Attention is drawn to the fact that most of the processes for anodic treatment and for numerous sealing and dyeing treatments are patented in this country. † For decorative purposes the best results are obtained with the wrought alloys Hiduminium RR56 and Hiduminium RR66, which, in the form of extruded bars, sections, and tubes, are supplied by the Reynolds Tube Co., Ltd., Birmingham. ‡ A special lubricant for this purpose is marketed by Alumilite Ltd., of Hammersmith, W. 6. HIGH DUTY ALLOYS LTD. SLOUGH Telephone: SLOUGH 822/3 Telegrams: "ALLOYS, SLOUGH" | ||